Internal combustion engines normally have at least one piston that is reciprocated within a cylinder. A rod connects the piston to a crankshaft that has offset portions. The offset portions of the crankshaft cause the end of the rod to orbit about an axis of the crankshaft. The rotation of the crankshaft drives a transmission or other load. Piston pumps operate in a similar manner, using a rotatably driven crankshaft to drive the piston.
One disadvantage of a conventional crankshaft is that the length of the stroke is fixed for a given crankshaft. Changing the length of the stroke will change the compression ratio, however this normally requires replacing the crankshaft. There are instances when a higher compression ratio is desired, such as at low load conditions, and instances when a lower compression ratio is desired, such as at high load conditions.
Proposals are shown in U.S. Pat. Nos. 5,908,014 and 4,860,702 for varying compression ratios of piston engines. Both of these patents utilize an eccentric at the rod end, the eccentric being connected to a gear train. The length of the stroke is selected by a gear arrangement that rotates the relative position of the eccentric to the gear train.